This invention relates to a self-cleaning printer and a self-cleaning print head.
Ink jet printers produce images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on a receiver medium such as a plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Many types of ink jet printers have been developed. One form of ink jet printer is the xe2x80x9ccontinuousxe2x80x9d ink jet printer. Continuous ink jet printers generate stream of ink droplets during printing. Certain droplets are permitted to strike a receiver medium while other droplets are diverted. In this way, the continuous ink jet printer can controllably define a flow of ink droplets onto the receiver medium to form an image. One type of continuous ink jet printer uses electrostatic charging tunnels that are placed close to the stream of ink droplets. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the receiver.
Another type of ink jet printer is the xe2x80x9con demandxe2x80x9d ink jet printer. xe2x80x9cOn demandxe2x80x9d ink jet printers eject ink droplets only when needed to form the image. In one form of xe2x80x9con demandxe2x80x9d ink jet printer, a plurality of ink jet nozzle is provided and a pressurization actuator is provided for every nozzle. The pressurization actuators are used to produce the ink jet droplets. In this regard, either one of two types of actuators are commonly used: heat actuators and piezoelectric actuators. With respect to heat actuators, a heater is disposed in the ink jet nozzle and heats the ink. This causes a quantity of the ink to phase change into a gaseous bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled onto the recording medium.
With respect to piezoelectric actuators, a piezoelectric material is provided for every nozzle. The piezoelectric material possesses piezoelectric properties such an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. When these materials are used in an ink jet print head, they apply mechanical stress upon the ink in the print head to cause an ink droplet to be ejected from the print head.
Inks for high speed ink jet printers, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9con demandxe2x80x9d type, must have a number of special characteristics. For example, the inks should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional xe2x80x9cspittingxe2x80x9d of ink droplets, the cavities and corresponding orifices are kept open.
Moreover, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices and print head surface are exposed to many kinds of airborne particulates. Particulate debris may accumulate on the print head surface surrounding the orifices and may accumulate in the orifices and chambers themselves. Also, ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. Of course, the particulate debris should be cleaned from the surface and orifice to restore proper droplet formation.
Ink jet print head cleaners are known. An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled xe2x80x9cIn Jet Print Head Face Cleanerxe2x80x9d issued Nov. 13, 1990 in the name of James C. Oswald an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and out an outlet. A vacuum source is attached to the outlet to create a sub-atmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. However, the use of heated air is not a particularly effective medium for removing dried particles from the print head surface. Also, the use of heated air may damage fragile electronic circuitry that may be present on the print head surface.
Cleaning systems that use a cleaning fluid such as an alcohol or other solvent have been found to be particularly effective when used to clean print heads. This is because the solvent helps to dissolve the ink and other contaminants that have dried to the surface of the print head. One way to use a cleaning fluid to clean a print head is known as wet wiping. In wet wiping, a cleaning fluid is applied to the print head and a wiper is used to clean the cleaning fluid and contaminants from the print head. Examples of various wet wiping embodiments are found in U.S. Pat. No. 5,914,734 by Rotering et al. Each of these embodiments uses a cleaning station to apply a metered amount of cleaning fluid to the print head and to wipe cleaning fluid and contaminants from the print head. However, wipers can damage the fragile electronic circuitry and Micro Electro-Mechanical Systems (MEMS) that may be present on the print head surface. Further, the wiper itself may leave contaminants on the surface of the print head that can obstruct the orifices.
Another ink jet print head cleaner is disclosed in commonly assigned U.S. Pat. No. 4,600,928 by Braun et al. Braun et al. shows a continuous ink jet printing apparatus having an ultrasonic print head cleaning system. During cleaning, the print head is moved to a cleaning area and a cleaning station is fixed to the print head. Once that the print head is so positioned, a meniscus of ink is supported proximate to the ink droplet orifices, a charge plate and/or an ink catcher surface. Cleaning is then accomplished by ultrasonically vibrating the meniscus. This cleaning can be enhanced by providing a fluid pressure differential in the meniscus to cause the meniscus to enter into orifices to be cleaned and to be released from the orifices. Once that the cleaning operation is completed, ink from the print head is ejected into a sump in the cleaning station.
U.S. Pat. No. 5,574,485 by Anderson et al. describes a cleaning station having a jet to define a flow of a cleaning fluid at the print head forming a meniscus bridge between the print head and the jet. Anderson teaches that the print head can be cleaned by agitating the meniscus bridge by use of an ultrasonic vibrator and removing the fluid by way of a pair of vacuum sources disposed on the cleaning station and flanking the jet.
In each of these patents, a cleaning station is needed to provide the cleaning action that cleans the print head. Such cleaning stations increase the weight, complexity and size of a self-cleaning printer.
It is, therefore, another object of the present invention to provide a self-cleaning printer and a self-cleaning print head that do not require a cleaning station to provide the cleaning action that cleans the print head.
It is a further object of this invention to provide a self-cleaning printer and self-cleaning print head that use a flow of a cleaning fluid to clean the surface of a print head.
The present invention comprises a self-cleaning printer having an orifice plate defining an ink jet orifice, a cleaning orifice and drain orifice. The orifice plate further defines an outer surface between the orifices. A source of pressurized cleaning fluid connected to the cleaning orifice and a fluid return is connected to the drain orifice. During cleaning operations, the source of pressurized cleaning fluid causes cleaning fluid to flow from the cleaning orifice, and the cleaning orifice directs the flow of cleaning fluid across the outer surface and the ink jet orifice and into the drain orifice.
The present invention also comprises a self-cleaning print head, comprising print head having an orifice plate defining an ink jet orifice, a cleaning orifice and a drain orifice. The orifice plate further defines an outer surface between the orifices. A supply of pressurized cleaning fluid is connected to the cleaning orifice and a fluid return is connected to the drain orifice. During cleaning operations, the source of pressurized cleaning fluid causes cleaning fluid to flow from the cleaning orifice, and the cleaning orifice directs the flow of cleaning fluid across said outer surface and the ink jet orifice and into the drain orifice.
In certain embodiments of the present invention, flow guides are defined on the surface of the print head. A cleaning member is also provided. In certain embodiments, the cleaning member comprises a splash guard that engages flow guides on the surface of the print head.